1. Field of the Invention
The present invention relates to an ink jet recording head used for an ink jet recording apparatus that performs recording by forming ink liquid droplets with ink to be discharged.
2. Related Background Art
A printer, a copying machine, a printing device for facsimile equipment, and the like, are structured to print images, which are formed by dot-patterns, on a printing medium (also called a recording sheet or a recording medium), such as paper, thin plastic plate, or cloth, in accordance with image information.
Printing apparatuses of the kind are divided into those of ink jet type, wire-dot type, thermal type, laser beam type, and others by the printing method adopted by each of them, respectively.
Of those apparatuses, the one that adopts ink jet method is such that it executes printing (recording) by discharging ink from the printing head to a printing medium. It can print highly precise images at high speed. Further, being of non-impact type, the printing apparatus adopting this method generates a lesser amount of noises, and also, among many advantages it has, it can print color images easily using multiple colors of ink. Of the ink jet methods, the so-called bubble jet method is particularly effective, in which ink is discharged from nozzle by means of bubbling energy exerted when ink is given film boiling by heater.
FIGS. 9A, 9B, and 9C are views that illustrate the conventional bubble jet type ink jet recording head (also, referred to as a “bubble jet printing head”). FIG. 9A is a plan perspective view that shows one of plural nozzles of the conventional head. FIG. 9B is a cross-sectional view taken along the line from the discharge port to the ink flow path represented in FIG. 9A. FIG. 9C is a cross-sectional view taken along line 9C—9C in FIG. 9B. Here, in FIG. 9B, the flow path formation member 107 is shown as a transparent member.
As shown in FIGS. 9A, 9B, and 9C, the bubble jet printing head is provided with a heater 102 on the upper layer of the base plate 101, which serves as electrothermal converting element. Then, on the base plate 101, there are arranged the bubbling chamber 103, which is a space that contains the heater 102, formed to face the arrangement surface of the heater 102; the ink discharge nozzle 104, which enables ink to be discharged from the bubbling chamber 103 in a specific direction; and the plate type flow path formation member 107 that faces the arrangement surface of heater 102 to form the supply path 106 to conduct ink from the supply chamber 105 to the bubbling chamber 103. Here, in this specification, the portion between the bubbling chamber 103 and the discharge port 108, which is an opening for discharging ink liquid droplet externally from the head, is defined as the ink discharge nozzle 104.
For the bubble jet type recording head described above, it is necessary to make the liquid droplet small so as to make the dot diameter formed on a printing medium small in order to attain printing in higher resolution. It is possible to make the liquid droplet small like this by downsizing the area of the discharge port, which is the opening at the tip of the ink discharge nozzle.
However, the following problem is encountered particularly when the liquid droplet is made small. With the area of discharge port being made small, the viscosity resistance is increased in the discharge direction, and there is a need for providing large power for operating discharges. The viscosity resistance can be expressed by the following equation (1).                                                                         Viscosity                ⁢                                                                   ⁢                resistance                            =                              η                ⁢                                                      ∫                    0                    1                                    ⁢                                                                                    G                        ⁡                                                  (                          x                          )                                                                    ⁢                                                                                           ⁢                                              ⅆ                        x                                                                                                            S                        ⁡                                                  (                          x                          )                                                                    2                                                                                                                                              η              ⁢                              :                            ⁢                                                           ⁢              ink              ⁢                                                           ⁢              viscosity              ⁢                                                           ⁢              S              ⁢                                                           ⁢                              (                x                )                            ⁢                              :                            ⁢                                                           ⁢              sectional              ⁢                                                           ⁢              area              ⁢                                                           ⁢                              G                (                x                )                            ⁢                              :                            ⁢                                                           ⁢              shape              ⁢                                                           ⁢              factor                                                          Equation  (1)            
Here, for example, the viscosity resistance becomes extremely high in the discharge direction if the diameter of discharge port is made smaller than Φ10 μm, and the problem of the kind is particularly encountered conspicuously. Also, with the increased flow resistance in the discharge direction, it becomes more difficult for ink to flow toward the discharge port side when bubbling occurs by use of the electrothermal converting element that serves as an energy generating element. It becomes rather easier for ink to flow toward the supply path side. As a result, the development of bubble is allowed to be larger to the supply path side. Conventionally, the development of bubble to the supply path side is suppressed to make the development easier to the discharge port side, and in order to increase the distribution of energy to the discharge port side, the width of flow path of the supply path on the side opposite to the discharge port side is made narrower. However, with the simple arrangement of making the width of flow path narrower, it takes more time inevitably to refill ink in the discharge port portion after the execution of discharge. As a result, the characteristics of discharge frequency (also, referred to as the “f characteristics”) are deteriorated.
Further, in a case where the electrothermal converting element is used as the energy generating element, and if it is required to provide large power for discharging the liquid droplet, which is arranged to be a smaller one, the temperature of element base plate is caused to rise due to the input of increased electric power. As a result, bubbling becomes instable to allow defective discharges to occur. Therefore, in order to prevent such temperature from rising, recording should be made slower at the sacrifice of more time to be taken. Then, a problem of slower speed recording is encountered.
Also, it is known that defective discharges of the ink jet recording apparatus may take place if dust particles are allowed to enter the discharge port portion and mixture thereof occurs therein. Conventionally, as the countermeasure to prevent the occurrence of defective discharges due to the mixture of such dust particles, there have been provided, as shown in FIG. 9A, the columns that serve as filters 109 at the entrance of the supply path 106 up to the height of the supply path 106 at specific intervals so as to prevent dust particles from being mixed.
To obtain the f characteristics, however, there is a need for making the height of the supply path larger as a structure needed to lower the flow resistance in the supply path, and also, the thickness (diameter) of each column that constitutes the filter 109 needs to be fixed in the height direction of the supply path. Therefore, as shown in FIG. 9B, the length of the gap between columns serving as filters 109 is determined by the height of the supply path 10, and in some cases, it may become impossible to provide sufficient filtering function as intended for the purpose. Also, the smaller the diameter of the discharge port, the smaller should be made the opening area of the filter. However, since the thickness (diameter) of each filter provided for the supply path is fixed eventually in the height direction of the supply path, there is no alternative but to simply make the gap between the columns constituting filters smaller. As a result, it becomes inevitable to take more time to refill ink in the discharge port after discharge. Thus, in some cases, the characteristics of discharge frequency (also, referred to as the “f characteristics”) are lowered after all.